"Based on the old, inaccurate dust numbers, which
erroneously
suggested that a medium-sized asteroid (1-2 km in diameter) could
cause
global climate change and famine, scientists calculated that
one's chance
of getting killed by an asteroid impact were about the same as
dying in a
plane crash. My new impact dust estimates indicate that death by
an asteroid
is far less likely and that such medium-sized asteroid impacts
would
not have catastrophic global effects. But of course the regional
effects
would still be devastating."
--Kevin Pope, 23 January 2002

The Geological Society of America issued a press release
yesterday which
will make the NEO community sit up and take notice. In it, Kevin
Pope
presents his new proposition according to which the impact of a
10-km sized
object on the Earth 65 million years ago did not, as is widely
assumed by
the impact research community, trigger a dust-connected 'cosmic
winter'.
Pope believes that "the original K-T impact extinction
hypothesis - the
shutdown of photosynthesis by submicrometer-size dust - is not
valid" for
the reason that it would require much more fine dust than has
been detected
in the K/T boundary layer.

Kevin Pope's conclusion is based on his reading of the
geophysical evidence,
in particular his attempt to measure the amount of small dust
particles in
the K-T boundary and to estimate the amount necessary for a
prolonged cosmic
winter. Whether his interpretation of a highly complex set of
data will hold
up to scientific scrutiny and critical analysis is uncertain.
What is
certain, however, is that the criticism of the impact winter
theory is no
new. Fore more than 10 years, the US geologist Dewey McLean has
been
pointing out much of the same deficiencies in the stratigraphical
record.
Since 1991, McLean has been suggesting that a K/T boundary impact
winter, if
it occurred at all, would have been "too transitory, or
feeble, to be
recorded in the geological record, and not of sufficient
magnitude to
trigger global biological catastrophe" (see his 1991 paper
"Impact winter in
the global K/T extinctions: no definitive evidences" below).

Kevin Pope, in contrast, does not question the cosmic winter
theory as such.
Instead, he conjectures that it may have been sulfate aerosols
produced from
impacted rocks and soot from global fires that could have shut
down
photosynthesis and caused global cooling. However, it is rather
questionable
whether these two mechanisms on their own would be capable of
triggering
global mass extinctions.

Pope does not limit his research to the analysis of small dust
particles in
the K/T boundary though. Instead of emphasising our lack of
knowledge and
existing uncertainties in the research on K/T and other
impact-related mass
extinctions, he seems convinced that the scientific community got
it
completely wrong and consequently blames it of "greatly
overstating the
impact hazard".

Perhaps Pope's most controversial claim is that even the impact
of a 2-km
sized asteroid or comet would only have regional, but not
globally
catastrophic effects. This attack is directly addressed at NASA
and its
Spaceguard Survey according to which the threshold for a global
impact
disaster lies somewhere in the region of a 1-km to 2-km sized
impactor (see
SPACEGUARD SURVEY UNDER FIRE: HAS NASA GREATLY OVERSTATED IMPACT
HAZARD?
below).

Disappointingly, Kevin Pope seems even more confused about the
recent media
reports regarding the close approach of asteroid 2001 YB5. None
of the press
and media reports mentioned any climatic impact effects
associated with this
object given the comparatively small sized of the near Earth
asteroid.

Be that as it may, I anticipate that Kevin's new paper will
stimulate
vigorous debate and trigger new research activities that will
eventually
help us to greatly improve our impact risk estimates. While I
remain rather
sceptical about his wider claims, I would be the first to greet
with relief
a firm verification of his calculations.

Scientists basically agree that an asteroid struck the Earth some
65 million
years ago and its impact created the Chicxulub crater in Yucatan,
Mexico.
More controversial is the link between this impact and a major
mass
extinction of species that happened at the geological (K-T)
boundary
marked by the impact.

But what mechanism did the impact trigger to cause mass
extinction? The
conventional theory is that impact dust obscured the sun,
shutting down
photosynthesis and snuffing out life. Kevin Pope from Geo Eco Arc
Research
shows in the February issue of GEOLOGY that the assumptions
behind this
theory are amiss, and therefore damage estimates from future
asteroid
impacts are also amiss.

This latter point became a recent issue when a large asteroid
passed near
the Earth on January 7 and news reports exaggerated its potential
impact
effects.

"Based on the old, inaccurate dust numbers, which
erroneously suggested that
a medium-sized asteroid (1-2 km in diameter) could cause global
climate
change and famine, scientists calculated that one's chance of
getting killed
by an asteroid impact were about the same as dying in a plane
crash," Pope
said. "My new impact dust estimates indicate that death by
an asteroid is
far less likely and that such medium-sized asteroid impacts would
not have
catastrophic global effects. But of course the regional effects
would still
be devastating."

To truly understand the influence of impact dust, scientists need
to find a
way to directly measure the amount of small dust particles in
such places as
the K-T boundary. In the meantime, Pope studied patterns of
coarse dust
particles to create a model that showed how the small dust
particles were
dispersed. Incorporating these geological observations with new
theoretical
work, Pope asserts that very few of the particles are of the size
that it
would take to shut down photosynthesis for any significant length
of time
and therefore the original K-T impact extinction hypothesis is
not valid. He
believes it may have been sulfate aerosols produced from impacted
rocks and
soot from global fires that could have shut down photosynthesis
and caused
global cooling.

"The original studies of the clay layer found at the K-T
boundary assumed
much or all of this layer was derived from fine impact
dust," he said. "More
recent studies of this layer have shown this not to be the case.
Furthermore, earlier estimates were based on extrapolations of
data from
surface atomic bomb blasts, which had about 100 million times
less energy
than the Chicxulub impact. Extrapolation over eight orders of
magnitude is
risky business."

Pope was involved in the "discovery" of the Chicxulub
crater in 1989-1990
when he worked at the NASA Ames Research Center. (Oil geologists
had
discovered the crater and reported the finding in 1981, but it
was basically
ignored.) He was using satellite images to map water resources in
the
Yucatan with Adriana Ocampo and Charles Duller when they found
the
semi-circular ring of sink holes. They thought the crater might
be the K-T
impact site and published their hypothesis in the May 1991 issue
of NATURE.

===============
(3) IMPACT DUST NOT THE CAUSE OF THE CRETACEOUS-TERTIARY MASS
EXTINCTION

Most of the 3-mm-thick globally distributed Chicxulub ejecta
layer found at
the Cretaceous-Tertiary (K-T) boundary was deposited as
condensation
droplets from the impact vapor plume. A small fraction of this
layer (<1%)
is clastic debris. Theoretical calculations, coupled with
observations of
the coarse dust fraction, indicate that very little (<1014 g)
was
submicrometer-size dust. The global mass and grain-size
distribution of the
clastic debris indicate that stratospheric winds spread the
debris from
North America, over the Pacific Ocean, to Europe, and little
debris reached
high southern latitudes. These findings indicate that the
original K-T
impact extinction hypothesis-the shutdown of photosynthesis by
submicrometer-size dust-is not valid, because it requires more
than two
orders of magnitude more fine dust than is estimated here.
Furthermore,
estimates of future impact hazards, which rely upon inaccurate
impact-dust
loadings, are greatly overstated.

Department of Geological Sciences
Virginia Polytechnic Institute and State University
Blacksburg, VA 24061

Abstract

About 66 million ago, Earth experienced a global extinction event
so
profound that it marks the boundary between the Mesozoic and
Cenozoic eras
and, on a finer scale, the Cretaceous (K) and Tertiary (T)
periods. Long the
topic of scientific inquiry and debate, the Cretaceous/Tertiary,
or K/T,
extinctions are cited as one of the top 10 to 20 unsolved
mysteries in
science. In the past decade, the debate has attracted scientists
from may
disciplines, and has expanded into one of the truly great debates
in the
history of science.

The K/T debate is a classic example of conceptual polarities, or
antitheses,
emerging from a common data base. The most fundamental polarities
involve
(1) extraterrestrial asteroid/comet impact versus terrestrial
volcanism as
causative factors in the extinctions, (2) sudden inpact-induced
catastrophe
spanning a few months to years versus gradual volcanic-induced
bioevolutionary turnover spanning several hundreds of thousands
of years,
and (3) "impact winter" via impact dust blasted into
the stratosphere
blocking out sunlight, and plunging Earth into darkness and
refrigeration
versus "greenhouse" warming via volcanic CO2 release
into the atmosphere
that triggered climatic warming, marine chemistry changes, and
ecosystem
collapses of a CO2-induced "greenhouse." The K/T debate
can only be resolved
by eliminating polarities.

This chapter addresses the latter polarity, and suggests that if
a K/T
boundary impact winter occurred, it was too transitory, or
feeble, to be
recorded in the geological record, and not of sufficient
magnitude to
trigger global biological catastrophe. On the other hand, a major
long-duration K/T transition carbon cycle perturbation associated
with
coeval climatic warming is indicated in the record. Throughout, I
will
discriminate between (1) short-duration K/T boundary impact-type
phenomena
that begin at the K/T contact and persist for a few months to a
few years,
and (2) long-duration K/T transition volcanic-type phenomena that
begin in
the Upper Cretaceous and persist into Early Tertiary, spanning
several
hundreds of thousands of years.

Small impacting objects that produce ordinary meteors or
fireballs dissipate
their energy in the upper atmosphere and have no direct effect on
the ground
below. Only when the incoming projectile is larger than about 10
m diameter
does it begin to pose some hazard to humans. The hazard can be
conveniently
divided into three broad categories that depend on the size or
kinetic
energy of the impactor:

Impacting body generally is disrupted before it reaches the
surface; most of
its kinetic energy is dissipated in the atmosphere, resulting in
chiefly
local effects.

Impacting body reaches ground sufficiently intact to make a
crater; effects
are still chiefly local, although nitric oxide and dust can be
carried large
distances, and there will be a tsunami if the impact is in the
ocean.

Large crater-forming impact generates sufficient globally
dispersed dust to
produce a significant, short-term change in climate, in addition
to
devastating blast effects in the region of impact.

The threshold size of an impacting body for each category depends
on its
density, strength, and velocity as well as on the nature of the
target. The
threshold for global effects, in particular, is not well
determined.

Category 1: 10-m to 100-m diameter impactors

Bodies near the small end of this size range intercept Earth
every decade.
Bodies about 100 m diameter and larger strike, on average,
several times per
millennium. The kinetic energy of a 10-m projectile traveling at
a typical
atmospheric entry velocity of 20 km/s is about 100 kilotons TNT
equivalent,
equal to several Hiroshima-size bombs. The kinetic energy of a
100-m
diameter body is equivalent to the explosive energy of about 100
megatons,
comparable to the yield of the very largest thermonuclear
devices.

For the 10-m projectiles, only rare iron or stony-iron
projectiles reach the
ground with a sufficient fraction of their entry velocity to
produce
craters, as happened in the Sikhote-Alin region of Siberia in
1947. Stony
bodies are crushed and fragmented during atmospheric
deceleration, and the
resulting fragments are quickly slowed to free-fall velocity,
while the
kinetic energy is transferred to an atmospheric shock wave. Part
of the
shock wave energy is released in a burst of light and heat
(called a
meteoritic fireball) and part is transported in a mechanical
wave.
Generally, these 100-kiloton disruptions occur high enough in the
atmosphere
so that no damage occurs on the ground, although the fireball can
attract
attention from distances of 600 km or more and the shock wave can
be heard
and even felt on the ground.

With increasing size, asteroidal projectiles reach progressively
lower
levels in the atmosphere before disruption, and the energy
transferred to
the shock wave is correspondingly greater. There is a threshold
where both
the radiated energy from the shock and the pressure in the shock
wave can
produce damage. A historical example is the Tunguska event of
1908, when a
body perhaps 60 m in diameter was disrupted in the atmosphere at
an altitude
of about 8 km. The energy released was about 12 megatons, as
estimated from
airwaves recorded on meteorological barographs in England, or
perhaps 20
megatons as estimated from the radius of destruction. Siberian
forest trees
were mostly knocked to the ground out to distances of about 20 km
from the
end point of the fireball trajectory, and some were snapped off
or knocked
over at distances as great as 40 km.

Circumstantial evidence suggests that fires were ignited up to 15
km from
the endpoint by the intense burst of radiant energy. The combined
effects
were similar to those expected from a nuclear detonation at a
similar
altitude, except, of course, that there were no accompanying
bursts of
neutrons or gamma rays nor any lingering radioactivity. Should a
Tunguska-like event happen over a densely populated area today,
the
resulting airburst would be like that of a 10-20 megaton bomb:
buildings
would be flattened over an area 20 km in radius, and exposed
flammable
materials would be ignited near the center of the devastated
region.

An associated hazard from such a Tunguska-like phenomenon is the
possibility
that it might be misinterpreted as the explosion of an actual
nuclear
weapon, particularly if it were to occur in a region of the world
where
tensions were already high. Although it is expected that
sophisticated
nuclear powers would not respond automatically to such an event,
the
possible misinterpretation of such a natural event dramatizes the
need for
heightening public consciousness around the world about the
nature of
unusually bright fireballs.

Category 2: 100-m to 1-km diameter impactors

Incoming asteroids of stony or metallic composition that are
larger than 100
m in diameter may reach the ground intact and produce a crater.
The
threshold size depends on the density of the impactor and its
speed and
angle of entry into the atmosphere. Evidence from the geologic
record of
impact craters as well as theory suggests that, in the average
case, stony
objects greater than 150 m in diameter form craters. They strike
the Earth
about once per 5000 years and -- if impacting on land -- produce
craters
about 3 km in diameter. A continuous blanket of material ejected
from such
craters covers an area about 10 km in diameter. The zone of
destruction
extends well beyond this area, where buildings would be damaged
or flattened
by the atmospheric shock, and along particular directions (rays)
by flying
debris. The total area of destruction is not, however,
necessarily greater
than in the case of atmospheric disruption of somewhat smaller
objects,
because much of the energy of the impactor is absorbed by the
ground during
crater formation. Thus the effects of small crater-forming events
are still
chiefly local.

Toward the upper end of this size range, the megaton equivalent
energy would
so vastly exceed what has been studied in nuclear war scenarios
that it is
difficult to be certain of the effects. Extrapolation from
smaller yields
suggests that the "local" zones of damage from the
impact of a 1-km object
could envelop whole states or countries, with fatalities of tens
of millions
in a densely populated region. There would also begin to be
noticeable
global consequences, including alterations in atmospheric
chemistry and
cooling due to atmospheric dust -- perhaps analogous to the
"year without a
summer" in 1817, following the explosion of the volcano
Tambora.

Comets are composed in large part of water ice and other
volatiles and
therefore are more easily fragmented than rocky or metallic
asteroids. In
the size range from 100 m to 1 km, a comet probably cannot
survive passage
through the atmosphere, although it may generate atmospheric
bursts
sufficient to produce local destruction. This is a subject that
needs
additional study, requiring a better knowledge of the physical
nature of
comets.

Category 3: 1 km to 5 km diameter impactors

At these larger sizes, a threshold is finally reached at which
the impact
has serious global consequences, although much work remains to be
done to
fully understand the physical and chemical effects of material
injected into
the atmosphere. In general, the crater produced by these impacts
has 10 to
15 times the diameter of the projectile; i.e., 10-15 km diameter
for a 1-km
asteroid. Such craters are formed on the continents about once
per 300,000
years. At impactor sizes greater than 1 km, the primary hazard
derives from
the global veil of dust injected into the stratosphere. The
severity of the
global effects of large impacts increases with the size of the
impactor and
the resulting quantity of injected dust. At some size, an impact
would lead
to massive world-wide crop failures and might threaten the
survival of
civilization. At still larger sizes, even the survival of the
human species
would be put at risk.

What happens when an object several kilometers in diameter
strikes the Earth
at a speed of tens of kilometers per second? Primarily there is a
massive
explosion, sufficient to fragment and partially vaporize both the
projectile
and the target area. Meteoric phenomena associated with high
speed ejecta
could subject plants and animals to scorching heat for about half
an hour,
and a global firestorm might them ensue. Dust thrown up from a
very large
crater would lead to total darkness over the whole Earth, which
might
persist for several months. Temperatures could drop as much as
tens of
degrees C. Nitric acid, produced from the burning of atmospheric
nitrogen in
the impact fireball, would acidify lakes, soils, streams, and
perhaps the
surface layer of the oceans. Months later, after the atmosphere
had cleared,
water vapor and carbon dioxide released to the stratosphere would
produce an
enhanced greenhouse effect, possibly raising global temperatures
by as much
as ten degrees C above the pre-existing ambient temperatures.
This global
warming might last for decades, as there are several positive
feedbacks;
warming of the surface increases the humidity of the troposphere
thereby
increasing the greenhouse effect, and warming of the ocean
surface releases
carbon dioxide which also increases the greenhouse effect. Both
the initial
months of darkness and cold, and then the following years of
enhanced
temperatures, would severely stress the environment and would
lead to
drastic population reductions of both terrestrial and marine
life.

2.3 Threshold Size for Global Catastrophe

The threshold size of impactor that would produce one or all of
the effects
discussed above is not accurately known. The geochemical and
paleontological
record has demonstrated that one impact (or perhaps several
closely spaced
impacts) 65 million years ago of a 10-km NEO resulted in total
extinction of
about half the living species of animals and plants (figure 2.3)
(Sharpton
and Ward, 1990). This so-called K-T impact may have exceeded 100
megatons in
explosive energy. Such mass extinctions of species have recurred
several
times in the past few hundred million years; it has been
suggested, although
not yet proven, that impacts are responsible for most such
extinction
events. We know from astronomical and geological evidence that
impacts of
objects with diameters of 5 km or greater occur about once every
10 to 30
million years.

Death by starvation of much of the world's population could
result from a
global catastrophe far less horrendous than those cataclysmic
impacts that
would suddenly render a significant fraction of species actually
extinct,
but we know only very poorly what size impact would cause such
mortality. In
addition to all of the known variables (site of impact, time of
year) and
the uncertainties in physical and ecological consequences, there
is the
question of how resilient our agriculture, commerce, economy, and
societal
organization might prove to be in the face of such an
unprecedented
catastrophe.

These uncertainties could be expressed either as a wide range of
possible
consequences for a particular size (or energy) of impactor or as
a range of
impactor sizes that might produce a certain scale of global
catastrophe. We
take the second approach and express the uncertainty as a range
of threshold
impactor sizes that would yield a global catastrophe of the
following
proportions:

It would destroy most of the world's food crops for a year, and
/or

It would result in the deaths of more than a quarter of the
world's
population, and/or

It would have effects on the global climate similer to those
calculated for
"nuclear winter", and/or

It would threaten the stability and future of modern
civilization.

A catastrophe having one, or all, of these traits would be a
horrifying
thing, unprecedented in history, with potential implications for
generations
to come.

To appreciate the scale of global catastrophe that we have
defined, it is
important to be clear what is not. We are talking about a
catastrophe far
larger than the effects of the great World Wars; it would result
from an
impact explosion certainly larger than if 100 of the very biggest
Hydrogen
bombs ever tested were detonated at once. On the other hand, we
are talking
about an explosion far smaller (less than 1 percent of the
energy) the the
K-T impact 65 million years ago. We mean a catastrophe that would
threaten
modern civilization, not an apocalypse that would threaten the
survival of
the human species.

What is the range of impactor sizes that might lead to this
magnitude of
global catastrophe? At the July 1991 Near-Earth Asteroid
Conference in San
Jaun Capistrano, California, the most frequently discussed
estimate of the
threshold impactor diameter for globally catstrphic effects was
about 2 km.
An estimate of the threshold size was derived for this Workshop
in September
1991 by Brian Toon, of NASA Ames Research Center. Of the various
enviromental effects of a large impact, Toon believes that the
greatest harm
would be done by the sub-micrometer dust launced into the
stratosphere. The
very fine dust has a long residence time, and global climate
modeling
studies by Covey and others (1990) imply significant drops in
global
temperature that would threaten agriculture worldwide. The
quanity of
sub-micrometer dust required for climate effects equivalent to
those
calculated for nuclear winter is estimated at about 10,000
Teragrams (Tg) (1
Tg = 1012g). For a 30 km/s impact, this translate to a threshold
impacting
body diameter of between 1 and 1.5 km diameter.

The threshold for an impact that causes widespread global
mortality and
threatens civilization almost certainly lies between about 0.5
and 5 km
diameter, perhaps near 2 km. Impacts of objects this large occur
from one to
several times per million years.

2.4 Risk Analysis

If this estimate of the frequency of threshold impact is correct,
then the
chances of an asteroid catastrophe happening in the near future
-- while
very low -- is greater than the probablility of other threats to
life that
our society takes very seriously. For purposes of discussion, we
adopt the
once-in-500,000 year estimate for the globally catastrophic
impact. It is
important to keep in mind that the frequency could be greater
than this,
although probably not by more than a factor of two. The frequency
could
equally well be a factor of ten smaller.

Because the risk of such an impact happening in the near future
is very low,
the nature of the impact hazard is unique in our experience.
Nearly all
hazards we face in life actually happen to someone we know, or we
learn
about them from the media, whereas no large impact has taken
place within
the total span of human history. (If such an event took place
before the
dawn of history roughly 10,000 years ago there would be no record
of the
event, since we are not postulating an impact large enough to
produce a mass
extinction that would be readily visible in the fossil record).
But also in
contrast to more familiar disasters, the postulated impact would
produce
devastation on a global scale. Natural disasters, including
tornadoes and
cyclones, earthquakes, tsunamis, volcanic eruptions, firestorms,
and floods
often kill thousands of people, and occasionally several million.
But the
civilization-destroying impact exceeds all of these other
disasters in that
it could kill a billion or more people, leading to as large a
percentage
loss of life worldwide as that experienced by Europe from the
Black Death in
the 14th century. It is this juxtaposition of the small
probability of
occurrence balanced against the enormous consequences if it does
happen that
makes the impact hazard such a difficult and controversial topic.

A 20-metre-long trench has mysteriously appeared on a remote
North Wales
mountain.

Astronomers say its possible the gash between Moel Eilio and
Snowdon may
have been caused by a meteorite.

It starts amid a cluster of smashed rock and ends in boggy ground
close to a
fence.

Another less likely theory is that it may have been caused by a
lightning
strike, reports the Daily Post.

Local walkers first noticed the disturbance, and runner Mike
Blake, from
Caernarfon, photographed it. He sent his images to the Natural
History
Museum and Jodrell Bank Observatory in Cheshire.

He said: "It's clear that some natural occurrence has taken
place, but what
exactly it was, I just don't know."

"It appears a rocky outcrop was hit and shattered, as there
are fragments
over a wide area. Leading away from it is a large gouge mark
about 20 metres
long, which ends in the boggy ground.

"I am desperately anxious to know what caused it, but one
thing is clear,
and that is that it was not caused by any vehicle."

Professor Mark Bailey, director of the Armagh Observatory in
Northern
Ireland, said: "There does appear to have been a violent
impact with the
mountainside. It would be wonderful if it were a meteorite
because we don't
get many of them in this part of the world, but something about
this does
not ring true. If it were a meteorite, it would almost certainly
have been
clearly visible."

Jay Tait, director of the Knighton Observatory in Powys, said:
"It is well
worth further investigation, and I shall be following this with
great
interest. If it were a meteorite, it would be virtually unique in
Wales, the
last one in England having been in the 1960s."

In CCNet 13/2002 - 23 January 2002 there was a post by Slaven
Garaj
"ELECTROPHONIC METEORS AND METEOR-ATMOSPHERE COUPLING".
I enjoyed reading
the post and the refered article in the Journal of Geophysical
Research. I
would like to congratulate authors of the article. It is the
first known
scientific confirmation of electrophonic sounds reality.

theory of "magnetic spagetti" relaxation in a wake of a
meteor can't explain
electrophonic sounds. Also it is interesting to find out that
authors of the article come to an idea, similar to the one, which
I
published first more than a decade ago, i.e. that a meteor is
probably just
a trigger of geophysical processes producing electrophonic sounds
in
specific geophysical conditions. I can just hope that in their
next article
they will mention this...

The CCNet 12/2002 - 21 January 2002, article that expressed a
hope for an
asteroid collision early warning system was commendable.
Populations might
then at least have a chance to evacuate to more survivable
locations. Also
most of the other articles about the sudden appearance of YB5 and
the
destructive nature of its brethren asteroids made good sense.
However, the
most important point was usually forgotten in the articles, and
the point is
partially a product of the evident fact that the appearance of
YB5 was
unexpected and sudden.

Moreover, YB5 beyond doubt proved that at a moment's notice we
might find
our planet on a collision course with a dangerous asteroid aiming
to smash
us. Furthermore, we might have just 25 days to defend our
children, the
Earth, and ourselves yet we have absolutely no defense prepared
to protect
the planet on such short notice from relatively numerous
asteroids like YB5.
Similarly, not even one nation intends to mount a defense against
such a
collision, or even gives lip service to what might be the most
common cosmic
collision scenario. Consequently, the most important point that
humanity
should have learned from our close encounter with YB5 is that we
need a
space defense plan and it must be implemented as soon as
possible, because
we are playing Russian Roulette with the Earth.

I suggest it would be a good thing for intelligent people to
think about a
rapid asteroid defense response, and propose space defense ideas
for comment
and criticism by way of an international Internet forum. Such a
dialogue
might initiate asteroid/comet defense concepts that could be
meaningful to
politicians responsible for national defense. The dialogue might
be designed
around the fact that unexpected / unpredictable asteroids like
YB5, which
are 200-400m NEO's, intent to collide with the Earth can be
defended
against. Unfortunately if they are critically larger we probably
couldn't do
much about a rapid defense and instead would have to run for the
hills or
hide in caves and holes in the ground until the catastrophe
subsided or we
might just die.

Correspondingly, I offer the following proposition through CCNet
that might
provide a sensible defense plan against the sudden unforeseen
emergence of a
random 200-300m destructive asteroid on a collision course with
our planet.
Furthermore, I welcome criticism as well as alternative arguments
and
contributory schemes designed to provide protection from
asteroids, or
comets, destined to collide with our world.

REPETITIVE FRAGMENTATION

The United States is currently developing an antimissile system
that is
intended to be used at a moment's notice. That system might
additionally be
modified by incorporating solid fuel boosters to provide a
multipurpose
defense. If modified it could quickly be used to launch rockets
with
multiple nuclear warheads that could be aimed at an approaching
asteroid as
well as hostile missiles.

An anti-asteroid nuclear warhead would have to be of a type that
could
penetrate into the hide of the hardest and densest asteroid. The
warhead
might be able to take advantage of natural fracturing on the
asteroid's
surface, possibly from the expansion and contraction resulting
from the
asteroid's journey around the Sun. The warhead might also be able
to take
advantage of a conglomerate type asteroid that is easily
shattered, but in
the long run the hardest and probably most dense asteroid must be
anticipated. Artillery projectiles designed to penetrate armor
plating using
hard heavy metal insertions, or even shaped explosive charges
have long been
used in warfare to penetrate bunkers and armor alike. Also
strategic bombs
capable of penetrating underground fortifications have been used
extensively, at least since my memories of the Vietnam War.

The U.S. Deep Impact mission is also experimenting with
detonating
explosives on at least one comet as reported by the BBC, 21
January 2002, "
On American Independence Day 2005, Deep Impact will reach its
target, the
six-kilometre diameter comet Tempel 1. The space probe will
release a
350-kilogram (770 lbs) projectile into the heart of the comet at
10
kilometres per second (six miles per second). It is expected to
blow a
crater the size of a football field and 20 metres (65 feet) deep.
The comet
will survive but should reveal the nature of its interior to add
to
scientific knowledge and to guide any future plans to deflect a
killer comet
with a nuclear nudge."

Nuclear explosive technology might already be taking advantage of
some form
of the armor/bunker penetration body of explosive knowledge that
seems to be
a part of the Deep Impact mission's exploding projectile. In any
event it
seems vital that the force of a nuclear explosion be concentrated
and
directed in order for it to break apart a 200-300m asteroid
especially one
that appears more dense and solid than others. Someone with more
knowledge,
about nuclear weapons and explosives, than I might offer
suggestions on this
important key element that is necessary to implement a repetitive
fragmentation asteroid defense plan.

Multiple rockets and warheads would be launched repetitively or
some even
almost simultaneously so they would be able to quickly bombard an
asteroid
until it fragmented. If one well placed explosion designed to
split apart
the asteroid did not fragment the space boulder then multiple
explosions
might be needed as a contingency. Moreover, after initial
fragmentation
remaining warheads must be able to retarget the asteroid's
resulting
consequential remains.

The warheads would have to retarget remotely or smartly, because
proper
targeting/bombardment, in a timely fashion, would determine the
fragmentation rate and subsequent size of the particles that
would
eventually hit the Earth. Consequently, as the succeeding
warheads
retargeted and bombarded the asteroid's remains, those fragments
would be
broken into smaller and smaller parts.

Given enough time, enough anti-asteroid rockets with successful
asteroid
splitting warheads, and continued asteroid fragmentation, the
once
destructive space object would be shattered into much smaller
pieces. Most
of the resulting collisions with the Earth would burn up in the
atmosphere
and those striking the ground would be of little consequence. On
the other
hand if the collisions were not inconsequential then they would
be
tolerable, and if not tolerable then at least preferable to a
single
catastrophic impact.

INTRODUCTION
Apollo asteroid 3102 Eger (1982 BB) is, so far, the only
confirmed E-type
object among the Near Earth Asteroid population. It was
discovered by M.
Lovas at the Piszkesteto Observatory, Budapest, Hungary, on
January 20,
1982.

LIGHTCURVE AND COLOR
>From visible photometric observation, Eger's lightcurve ( LC
) was found to
have an amplitude from 0.7 to 0.9 magnitudes. Rotation Period =
5.70 Hours.
Variations between its visual and thermal infrared LCs were
compared. Both
were in-phase and this fact indicated Eger is an object were body
shape is
the primary cause of the LC's amplitude. Variation was found to
be due
primary to an elongated body shape rather than to albedo
variations across
its surface.
Color : V - R = 0.48 , R - I = 0.42 , [1,2,3,4].

COMPOSITION
Reflectance spectra ( 0.8 to 2.5 micrometers ) were obtained
using NASA
Infrared Telescope on Mauna Kea , Hawaii, USA, in 1991. Its
spectrum showed
no specific mineral absorption features wich was found
consistent, together
with a very high albedo ( 0.41 to 0.49 ), with the
spectra of well known E-Type asteroids. The E-class asteroids
have high
albedos, neutral colors and nearly featureless spectra. They have
been
interpreted to be assemblages composed of some Iron-free silicate
mineral,
probably Enstatite, Forsterite, or Feldspar. Most researchers
believe
E-class objects are analogous to the Enstatite achondrite
meteorites
(aubrites), [3].

RADIOMETRY
Thermal infrared radiometry was used to determine Eger's
properties:
Albedo = 0.53 to 0.63 . Eger is very bright!.
Diameter = 1.4 to 1.5 km..
Again, its very high albedo matches well with an E-class
asteroid,[5].

RADAR STUDIES
Radar measurements and studies of 1982BB were made from Arecibo
Observatory,
Puerto Rico, and at Goldstone Observatory, California, USA in
1986 and 1996.
Both the 305-m and the 70-m antennas were used to run radar
experiments in
2380 MHz and 8510 MHz respectively. Asymmetric radar spectra were
found to
be clear evidence of an elongated shape for Eger. Its shape was
modeled as a
2.3 X 1.5 km biaxial ellipsoid. Eger's radar albedo was
found consistent
with an E-type object and this asteroid's surface was found to be
extremely
rough at centimeter to meter scales.[6].

It is a fragment of the crust and/or mantle of a bigger parent
body composed
of highly reduced materials. That body was extensively melted and
magmatically differentiated so most of its metal was separated
from the
silicates. Then, after a catastrophic collision, Eger was ejected
from its
parent body. Parent body was a member of the Main Belt.

Part of the argument used to support the notion that life may
have arisen on
Mars early in its history depends on the presence of carbonates
in the
notorious meteorite ALH84001 found in Antarctica. Supposedly
having been
ejected by an impact on the Martian surface (based on its oxygen
isotope
composition and the blend of noble gases trapped within it),
ALH84001 also
contains the minute structures that were prematurely announced in
a blaze of
publicity as fossilized alien life forms by US and British
meteorite
specialists in 1996. The discoverers claimed that carbonate
minerals within
it clearly evidenced the rotting of silicates by liquid water
containing
dissolved CO2; so they do in terrestrial rocks. However,
carbonates also
occur in meteorites that by no shred of the imagination can have
formed
within sizeable planets. Many probably accreted in a near vacuum
from dusts
that occur in clouds within our galaxy, while the solar system
was forming.

Using infrared spectra to assess the mineral composition of dust
clouds
surrounding stars, a team of European and American cosmochemists
has found
that in two cases such dust contains calcite and perhaps dolomite
(Kemper,
F. et al. 2002. Detection of carbonates in dust shells
around evolved
stars. Nature, v. 415, p. 295-297). Because liquid water
cannot exist in a
near vacuum, production of these carbonates cannot have taken
place by the
familiar silicate-rotting process. More likely, they formed
on the surfaces
of silicate dust or ice grains by reactions between calcium and
magnesium
ions and those in which carbon and oxygen were combined.

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